Method and device for producing highly condensed polyesters in the solid phase

ABSTRACT

The present invention relates to a method for producing solid-state polycondensed polyesters by using crystallization with or without subsequent solid-state polycondensation for producing bottles, sheets, films, and high-tenacity technical filaments.

The present invention relates to an apparatus and a continuous ordiscontinuous method for producing solid-state polycondensed (highlycondensed) polyesters by using crystallization with or without asubsequent solid-state polycondensation for producing bottles, sheets,films and high-tenacity technical filaments.

The known aromatic polyesters or copolyesters, in particularpolyethyleneterephthalate and the copolymers thereof with small amountsof e.g. isophthalic acid or cyclohexanedimethanol,polybutyleneterephthalate, polytrimethyleneterephthalate,polyethylenenaphthalate and the copolyesters thereof, which serve as rawmaterial for fibers, films and packaging, are prepared such that thepolyester melt in the melt polycondensation stage is brought to a meanend viscosity. The mean degree of polycondensation, expressed inintrinsic viscosity (I.V.), ranges from 0.30 to 0.90 dl/g inpolyethyleneterephthalate and its correspondingly low-modifiedcopolyesters after melt polycondensation.

Since the production of granules with an I.V. above 0.65 dl/g is hardlypossible, in particular in conventional autoclaves, and highviscosities >0.80 dl/g entail a considerable capacity reduction in meltpolycondensation and since, moreover, the polyesters used for foodpackaging require a very low acetaldehyde value, the meltpolycondensation in the prior art is followed by a solid-statepolycondensation (SSP) which leads to an increase in I.V. in general by0.05-0.4 dl/g and to a reduction of the acetaldehyde content of about25-100 ppm to values <1 ppm in the PET.

In this solid-state polycondensation following the melt polycondensationstage, the mean viscosity is thus raised such that the strength requiredfor the corresponding field of application is achieved, the acetaldehydecontent in the case of food packaging is reduced in accordance with therequirements, and the exiting oligomer content is lowered to a minimumamount. It is here important that the acetaldehyde, which is bound asvinyl ester, also called depot acetaldehyde, is decomposed to such adegree that during processing of the polyester granules into packaging,in particular polyester bottles, according to the stretch blow andinjection stretch blow method, only a minimum amount of acetaldehyde isre-developed (re-formed) in the polyester. Especially when mineral wateris filled into polyester bottles, less than 2 ppm acetaldehyde should becontained in the bottle wall consisting of polyethyleneterephthalate.

Apart from SSP, methods are known for the dealdehydization ofpolyethyleneterephthalate by treatment with nitrogen or dry air, asdescribed in U.S. Pat. No. 4,230,819. To obtain the required lowacetaldehyde content in the material, temperatures of up to 230° C. areused. When air is used, a strong thermooxidative decomposition of thepolyester must be expected at such elevated temperatures. When nitrogenis used, the costs for gas and complicated purification are increased.

U.S. Pat. No. 4,223,128 excludes temperatures of more than 220° C. whenair is used as the carrier gas. Described is the desired increase inI.V. with the help of large amounts of dry air at a dew point of 40 to−80° C. At the treatment temperature of 200° C. as outlined in theexamples of this patent, oxidative damage to individual grains of thegranulate cannot be ruled out in continuous methods, which have a moreor less wide range of residence times.

SSP achieves a chain extension of the polyesters in the solid state forkeeping the side reactions, which occur to a stronger degree in a melt,as small as possible, as well as a removal of the harmful by-products.With this chain extension, which is expressed by an increase in I.V., itis possible to produce products, such as bottles or tire cord, whichrequire an increased strength.

However, since polyesters are partly crystalline thermoplasticmaterials, they have a more or less large amorphous amount, depending onthe type. When SSP is carried out, this fact poses problems because theamorphous amounts at the temperatures required for SSP lead to sticking,which may even lead to a standstill of the production plant.

Therefore, it is also known that as a precursor to SSP a crystallizationof the partly crystalline chips from the melt polycondensation iscarried out for preventing any tendency to sticking under nitrogen orair atmosphere, at temperatures between 160-210° C., as described inU.S. Pat. Nos. 4,064,112, 4,161,578, and 4,370,302.

WO 94/17122 discloses a 2-stage crystallization with preheating andintermediate cooling prior to SSP to prevent sticking. The described SSPtemperature ranges from 205° C. to 230° C.

For improving the quality of the chips, it is possible to use, asdescribed in JP 09249744 or U.S. Pat. No. 5,663,290, a moist inert gasbefore or during SSP, or—as disclosed in U.S. Pat. No. 5,573,820—thechips may previously be treated with hot water or directly with watervapor intensively at temperatures of up to 200° C. prior tocrystallization. In this case, however, a strong undesired drop in I.V.by hydrolysis in the PET must already be:expected at the standardtemperatures of >190° C.

A further method is the treatment of the chips to be crystallized withpurified non-dried nitrogen from SSP in countercurrent flow in thesecond crystallization stage, as outlined in EP 222 714. The effectdescribed therein for reducing the acetaldehyde content is ratherevaluated as insignificant.

These crystallization steps aim at reducing the amorphous amount of thepolyester to such an extent that SSP can be carried out without anysticking.

The basic differences between the performance of SSP and ofcrystallization are:

-   -   1. that the residence times in the case of crystallization are        much shorter than in SSP, 3 h on the average compared to 540 h,        and    -   2. in the case of crystallization physical processes prevail, as        becomes e.g. apparent from the normally very slight rise in I.V.        from 0.01 to 0.02 dl/g, while chemical reactions take place in        the case of SSP, as can be seen from a rise in I.V. of normally        0.2 to 0.3 dl/g.

It is therefore the object of the present invention to provide a methodfor producing solid-state polyesters, which method can be carried outeasily and simultaneously helps to maintain or improve the particularlyhigh quality standards demanded from polyesters for packaging withrespect to color, molar mass distribution, acetaldehyde content,acetaldehyde re-developing, oligomer amount and tendency to sticking,and to significantly reduce waste and dust formation.

According to the invention this object is achieved by a method forproducing polyesters, comprising

-   -   crystallization of a polyester material, characterized in that        crystallization is carried out in two stages, wherein    -   in the first stage partly crystalline polyester material is        provided, and    -   in the second stage, the partly crystalline polyester material        flows at temperatures suited for crystallization (i) under        mechanical disturbance and gas in countercurrent flow, (ii)        under mechanical disturbance and gas in concurrent flow,        and (iii) without mechanical disturbance and gas in concurrent        flow.

The present method is suited for making granules of partly crystallinearomatic polyesters or copolyesters, obtainable from one or moredicarboxylic acids or the methylesters thereof, such as terephthalicacid, isophthalic acid, naphthalinedicarboxylic acid and/or4,4-bisphenyidicarboxylic acid, and one or more diols, such asethyleneglycol, propyleneglycol, 1,4-butanediol,1,4-cyclohexanedimethanol, neopentylglycol, and/or diethyleneglycol.

These starting compounds can be processed in a way known per seaccording to the continuous or discontinuous method of esterification orinteresterification using known catalysts with a subsequent meltpolycondensation under vacuum to obtain polyester material, preferablygranules.

Preferably, polyethyleneterephthalate homopolymers and copolymers areused with a comonomer content of less than 10% by wt.

In the first stage of the method according to the invention, partlycrystalline polyester material is provided. Preferably, the partlycrystalline polyester material has a degree of crystallization of about40-48%.

For providing the polyester material in the first stage of the methodaccording to the invention, any suitable and partly crystallinepolyester material may be used. The partly crystalline polyestermaterial may be obtained by crystallization of a polyester materialobtained from melt polycondensation. Preferably, to provide thepolyester material in the first stage of the method according to theinvention, amorphous polyester material obtainable after meltpolycondensation, preferably granulate, is treated in the first stagefor increasing the degree of crystallization to about 40 to about 48%under vortexing by way of a gas flow at suitable temperatures andresidence times. Preferred temperatures range from about 170 to about210° C., and preferred residence times amount up to about 30 min,preferably about 10 to about 30 min.

The gas used for vortexing is preferably air and/or nitrogen.

The partly crystalline polyester material is preferably produced bymeans of a fluidized bed reactor. In particular, the first stage ofcrystallization is carried out in-two zones, the crystallization in thefirst zone 1 being performed in a fluidized bed with mixing properties,and in the second zone 2 in a fluidized bed with controlled granulateflow.

FIG. 1 shows a preferred embodiment of a fluidized bed reactor 20 withwhich the crystallinity of a polyester granulate is raised to thedesired degree, in particular to 40-48%. The granulate is here conveyedby a conveying device 10 into a fluidized bed crystallizer 20 equippedwith rectangular fluidization surfaces and with two zones 30, 50, inwhich the granulate is crystallized at rising temperatures of 170-210°C. and, optionally, under dry gas at a dew point of 20 to −50° C.

The gas/chip ratio-may be 3-4 in the first zone and 2-3 in the secondzone, at a residence time of 10-30 min.

As shown in FIG. 1, the gas can be-guided such that the gas by beingdistributed over a perforated sheet passes into the first zone 30 via agas inlet opening 40 at a gas rate of 3.24 m/sec and into the secondzone 50 via a gas inlet opening 40′ at a gas rate of 2.1-2.7 m/sec(velocity in empty space) and leaves the crystallizer again via a jointgas outlet 60 in the upper region. This way of guiding the gas effects afluidized bed with mixing properties in the first zone 30 and to avortexing with controlled granulate flow in the second zone 50. The dustamount at the outlet of the crystallizer is <10 ppm.

The granulate obtained after the first stage of crystallization haspreferably a degree of crystallization in the chip of about 40-48%.

The partly crystalline polyester material which can be used according tothe invention, preferably granulate, flows in a second stage attemperatures suited for crystallization (i) under mechanical disturbanceand gas in countercurrent flow, (ii) under mechanical disturbance andgas in concurrent flow, and (iii) without mechanical disturbance and gasin concurrent flow.

“Flowing” of the polyester material in the sense of the presentinvention means a movement of the polyester material in one direction,the movement being e.g. effected by gravitation and/or mechanicaltransportation.

Steps (i) to (iii) of the second stage of the method according to theinvention are carried out particularly preferably in a continuous way,i.e., the polyester material passes through steps (i) to (iii) in acontinuous flow. The polyester material, however, may also be treated inbatches in steps (i) to (iii). Preferably, steps (i) to (iii) arecarried out in the indicated sequence. However, it is also possible tocarry out steps (i) to (iii) in any other sequence.

The gas used in the second stage (i) to (iii) is preferably air ornitrogen, in particular nitrogen.

The temperature suited for crystallization in the second stage (i) to(iii) is preferably about 190 to about 220° C., more preferably 190 to215° C., and particularly preferably 200 to 210° C.

The residence time of the polyester material in the second stage (i) ispreferably about 30 to about 60 min, in the second stage (ii) about 30to about 60 min, and in the second stage (iii) about 60 to about 180min.

The second stage of crystallization is particularly preferably carriedout in three zones of a shaft type crystallizer, namely zones 3, 4 and5, in which steps (i) to (iii) of the second stage are carried out. Inzone 3, the granules are subjected under periodically arising mechanicaldisturbance with gas in countercurrent flow, in zone 4 underperiodically arising mechanical disturbance with gas in concurrent flow,and in zone 5 under no mechanical disturbance and gas in concurrentflow.

The second stage of crystallization is preferably carried out in anapparatus according to the invention for producing polyesters. Theapparatus (70) according to the invention for crystallizing polyestermaterial in granular form, e.g. a shaft type crystallizer, comprisesthree successive sections (80, 90, 100), at least one inlet opening(110) provided in the first section (80), at least one outlet opening(12) provided in the third section (100), a means for effectingmechanical disturbance of the polyester material (130), which isprovided in the first and second sections (80, 90), at least one gasinlet opening (140) arranged in the transitional area from the first tothe second section, and at least one gas outlet opening (150, 160) whichis provided both in the first and third section.

In a preferred embodiment, the apparatus according to the inventioncomprises a means for generating a periodic mechanical disturbance (130)with a shaft (170) that has provided thereon-at least one, preferablysix or more, arms (180, 180′), which effect a periodic mechanicaldisturbance of the flowing polyester material by rotation of shaft(170). The means may also comprise a first shaft and a second shaft, atleast one arm being provided on each shaft.

FIG. 2 shows a preferred embodiment for an apparatus according to theinvention, namely a shaft type crystallizer 70, in which the secondstage of the method according to the invention can be carried out. Thegranulate is introduced in the second stage, as shown in FIG. 2, into acontinuously operating, vertically standing three-part shaftcrystallizer 70 having a centered rotatable shaft 170 installed in thelongitudinal axis. In the first and second section 80, 90 of the shaftcrystallizer, zones 3 and 4, arms 180, 180′ are mounted on the shaft atspecific intervals and with a small flow resistance, the shaft effectinga periodic mechanical disturbance of the bulk material. Due to themovement of the granules, the formation of agglomerates (sticking) ofthe material is prevented. In the third section 100 of the shaft typecrystallizer, the granules are treated in zone 5 without anydisturbance.

In the third and fourth zone, the granules are disturbed mechanicallyand periodically, while in the fifth undisturbed zone the residence timeis made uniform at a beginning postpolycondensation.

The gas is guided such that it is supplied between the third and fourthzone (first and second section of the shaft crystallizer) via a gasinlet opening 140 and leaves the crystallizer again in the upper orfirst section 80 via a gas outlet opening 150 and in a proportionateamount also in the lower or third section 100 via a gas outlet opening160. The gas is here guided in the third zone (first section of theshaft crystallizer) in countercurrent flow with respect to the granulesand in the fourth and fifth zone in concurrent flow (second and thirdsection of the shaft crystallizer).

The gas outlet openings (150, 160) are here preferably arranged suchthat the gas introduced via the gas inlet opening (140) is guided withthe granules in countercurrent or concurrent flow as long as possible,i.e. at the beginning of the first section (80) and at the end of thethird section (100) of the shaft crystallizer (70).

In the third zone (first section 80 of the shaft crystallizer 70), thePET granules are heated under periodically acting mechanical disturbancepreferably with hot gas, in particular nitrogen, in countercurrent flowwith respect to the granules at a gas-chip ratio of 1-3 and at aresidence time of 30-60 min to 1 90-220° C.

In the fourth zone (second section 90 of the shaft crystallizer 70), thePET is further crystallized and made uniform under periodically actingmechanical disturbance preferably at 190-220° C. with the gas, inparticular nitrogen, in concurrent flow at a gas-chip ratio of 0.5-1.The residence time is 30-60 min.

The PET granules treated in this way in the third and fourth zone arepreferably treated in the undisturbed fifth zone (section 100 of theshaft type crystallizer 70) at a temperature of 190-215° C. inconcurrent fashion at a gas/chip ratio of 0.1-1 in such a way that at amean residence time of 60-180 min, a slight postpolycondensation alreadytakes place in said zone, apart from aldehyde reduction andcrystallization. According to the method of the invention, the tendencyto sticking of the granules is thereby reduced considerably.

The total residence time of the polyester material in the first andsecond stage of crystallization, provided that it includes theabove-described zones 1 to 5, is preferably between 100-350 min,particularly 130-330 min, the residence time ratio in the first stage incomparison with the residence time in the second stage being 1:4 to1:32. Particularly preferably, the residence time ratio in the first andsecond stages of crystallization, on condition said stages comprisezones 1 to 5, has a residence time in zones 3 and 4 that is 4 to 6 timeslonger than in zones 1 and 2, and a residence time in zone 5 that is 2to 3 times longer than in zones 3 and 4.

The polyester material used in the method of the invention haspreferably an I.V. of at least about 0.3 dl/g, more preferably about 0.3dl/g to about 0.9 dl/g, even more preferably about 0.3 dl/g to 0.8 dl/g,particularly preferably about 0.66 dl/g to 0.9 dl/g, particularly about0.72 to 0.8 dl/g. Particularly preferably, a polyester material is usedthat has an I.V. of at least about 0.66 dl/g, more preferably about 0.66to 0.8 dl/g, and particularly about 0.72 to 0.8 dl/g, because thematerial obtained thereby has a desired low content of acetaldehyde,namely <10 ppm, particularly <1 ppm, and is therefore suited for furtherprocessing without subsequent SSP into polyester molded articles inwhich a low acetaldehyde content is required, e.g. bottles. Surprisinglyenough, it has now been found that polyester material, such asgranulate, can be used with a high I.V. when the method according to theinvention is carried out.

When polyester material with an I.V. of at least about 0.3 dl/g to about0.72 dl/g is used, SSP is preferably carried out thereafter.

Since partly crystalline-polyester during crystallization in thecrystallizer and in the subsequent solid-state polycondensation reactormay tend to form agglomerates to an increased degree due to a highexothermal heat development, and since such sticking may be so strongthat they no longer separate from one another when standardcrystallization and solid-state polycondensation methods are employed,the use of spherical polyester material is preferred in the methodaccording to the invention. However, it is also possible to use othergranular shapes, such as cylindrical or scale-like granules.

Cylindrical granules, however, are not preferred because they easilystick together because of the surfaces and edges, and wear is increased.Due to the asymmetry of the cylindrical chips, a uniform crystallizationfrom the exterior to the core of the chip is difficult. In comparisonwith the balanced cylindrical chip, the use of approximately sphericalchips offers the advantage of a more uniform crystallization, animproved molar mass distribution in the chip, and a bulk weight that ishigher by 5 to 10%. The dust amount which is lower when spherical chipsare used must be regarded as a further essential advantage.

Particularly preferably, the granules used have a surface of 1.45-2.0m²/kg, preferably 1.50 to 1.85 m²/kg.

The granules obtained with the method according to the invention havepreferably a uniform degree of crystallization of about 49 to about 53%,in particular about 52%, and are pretreated in this crystallizationtechnique such that a sticking of the PET granules due to exothermalreactions in a possibly subsequent solid-state postcondensation isavoided.

The granules-obtained according to the invention have an acetaldehydecontent of <10 ppm, particularly preferably 0.5-5 ppm, and particularly<1 ppm.

The dust amount of the granules is preferably <10 ppm aftercrystallization according to the invention.

Surprisingly enough, it has been found that upon application of themethod according to the invention with the 2-stage crystallization, inparticular by using a fluidized bed and shaft type crystallization, apolyester granulate can be produced with a low acetaldehyde value, asmall acetaldehyde reformation, excellent color brilliance, very lowdust values, without sticking and upon use of chips with a high I.V.between 0.66-0.90 dl/g from melt polycondensation, a subsequentsolid-state polycondensation can be omitted.

The granules obtained according to the invention have preferably an I.V.variation of less than 1.5%.

Moreover, the present invention relates to a method for producingpolyester molded articles, polyester material, in particular granules,being obtainable according to the method of the invention without anysolid-state polycondensation.

In particular, polyester material, especially in the form of granules orchips, which was produced with the method according to the invention andwith an I.V. from melt polycondensation of >0.66 dl/g, can directly besupplied without any further condensation in a solid-statepolycondensation reactor to processing in the stretch blow or injectionstretch blow method for producing polyester molded articles. On theother hand, the polyester material of a lower I.V. can be subjectedafter melt polycondensation and the crystallization method according tothe invention in a subsequent step to a standard solid-statepolycondensation which operates continuously or discontinuously, and canthen be used for producing polyester molded articles.

The polyester molded articles are preferably selected from the groupconsisting of bottles, sheets, films and high-tenacity technicalfilaments.

The invention shall now be described in more detail with reference to afew embodiments that are not limiting in any way. The characteristicvalues as indicated were here determined as follows:

The intrinsic viscosity (I.V.) was measured at 25° C. in a solution of500 mg polyester in 100 ml of a mixture consisting of phenol and1,2-dichloirobenzol (3:2 weight parts).

The COOH terminal group concentration was determined by means ofphotometric titration with 0.05 ethanolic potash lye versus bromothymolblue of a solution of a polyester in a mixture of o-cresol andchloroform (70:30 parts by weight).

Diethylenegylcol (DEG), isophthalic acid (IPA), and1,4-cyclohexanedimethanol (CHDM) are determined in the polyester bymeans of gas chromatography after a preceding methanolysis of 1 gpolyester in 30 ml methanol with addition of 50 mg/l zinc acetate in asealed tube at 200° C.

The measurement of the turbidity value in “nephelometric turbidityunits” (NTU) was carried out in a 10% by wt. solution of polyester inphenol/dichlorobenzol (3:2 parts by wt.) with a nephelometer of thecompany Hach (type XR, according to U.S. Pat. No. 4,198,161) in a cuvethaving a diameter of 22.2 mm, by analogy with the DIN standard 38404,part 2, which is usual for water. The intensity of the stray light ismeasured in comparison with a formazin standard solution less the valueof the solvent (about 0.3 NTU).

The color values L and b were measured according to HUNTER. Thepolyester chips were first crystallized in the drying oven at 135±5° C.for one hour. The color values were then determined by measuring the hueof the polyester sample in a three-range color meter with threephotocells, having each arranged upstream thereof red, green and bluefilters (X-, Y- and Z-values). Evaluation was carried out according toHUNTER's formula, where $\begin{matrix}{L = {10\left. \sqrt{}Y \right.\quad{and}}} \\{b = \frac{7,0}{\left. \sqrt{}Y \right.\quad\left( {{Y - 0},{8467\quad Z}} \right)}}\end{matrix}$

The acetaldehyde was expelled by heating in a closed vessel frompolyester and the acetaldehyde was determined in the gas chamber of thevessel by gas chromatography with the headspace injection system H540,Perkin Elmer; carrier gas: nitrogen; column: 1.5 m special steel;filling Poropack Q, 80-100 mesh; sample amount: 2 g; heatingtemperature: 150° C., heating duration: 90 min.

For the determination of the acetaldehyde re-developing rate, PET chipswere ground and the ground material was molten in a thermodesorber underdefined conditions (300° C. and three residence times: 12-25 min). Thecontent of the resulting acetaldehyde adsorbed on Tenax was thendetermined by gas chromatography.

The dust analysis is carried out by gravimetry. To this end 1 kg of thechips is washed with methanol, the washing agent is filtered off via afilter and the residue is dried and weighed.

EXAMPLE 1 Comparison

In Example 1, approximately amorphous cylindrical chips with a weight of15.5 mg/chip and a surface of 1.85 m²/kg, a bulk weight of 790 kg/m³ andan I.V. of 0.612 dl/g, were crystallized from the melt polycondensationmethod for producing slightly modified PET for bottles to be filled withcarbonated soft drinks (CSD), water or other filling media and subjectedto solid-state polycondensation.

EXAMPLE 2

In Example 2, approximately round chips with a weight of 15.5 mg, asurface of 1.55 m²/kg and a bulk weight of 840 kg/m³ were used andcrystallized and then subjected to solid-state polycondensationaccording to standard methods, in accordance with the method accordingto the invention.

Material used in Examples 1 and 2:

Catalyzer content Sb: 200 ppm, phosphor content 17 ppm, cobalt: 15 ppm,blue dye: 0.5 ppm, IPA: 2% by wt., DEG: 1.3% by wt.

The results of Example 1 are shown in Table 1.1 and the results ofExample 2 in Table 1.2. TABLE 1.1 Example 1 (standard crystallizationwith subsequent SSP) 1. 2. Crystallizer Crystallizer Material fluidizedbed blade type SSP used: crystallizer crystallizer VWZ: 12 h cylindricalVWZ: VWZ: T: 208.5° C. chip 60 min. 75 min delta I.V. = Analyses shapeT: 200° C. T: 219° C. 0.200 [dl/g] I.V. [dl/g] 0.612 0.617 0.621 0.812COOH 27 28 26 28 [mmol/ kg] DSC: 250/143/78 250.5/145/79.7 Tm/Tk/Tg [°C.] Color L 82.7 84.9 87.7 89 Color a −1.6 −1.4 −1.4 −1.4 Color b −3.6−0.8 −0.7 −0.5 AA [ppm] 45 9.1 3.5 0.5 KTG [° C.] — 48.5 51 55.6 AA- —9.7 reformation [ppm] Dust — <10 >500 >500 [ppm]VWZ = residence time,T = temperature

TABLE 1.2 Example 2 2. Crystallization 1. shaft type Crystallizationcrystallizer SSP Material (zone 1 und 2) (zones 3 to VWZ: used:fluidized bed 5) 12 h spherical crystallizer VWZ: T: 207.5° C. chip VWZ:60 min 180 min delta I.V. = Analyses shape T: 200° C. T: 215° C. 0.240[dl/g] I.V. [dl/g] 0.602 0.616 0.636 0.842 COOH 30 27 26 26 [mmol/kg]DSC 250/143/ — — 251/145/80.1 Tm/Tk/Tg 78.4 [° C.] Color L 83 85.1 88.189.4 Color a −1.7 −1.4 −1.3 −1.3 Color b −3.3 −1.0 −0.6 −0.6 AA [ppm] 558.8 1 0.2 KTG [° C.] — 46.1 53.1 55.2 AA- — 9.3 reformation] Dust <10<10 <10 <10 [ppm]

EXAMPLES 3 AND 4

In a further test, approximately round chips with a weight of 15.5 mgand a surface of 1.55 m²/kg, a bulk weight of 840 kg/m³ and a high I.V.of 0.79-0.80 dl/g, produced according to the melt polycondensationmethod, were processed with two different catalyzer systems according tothe crystallization method of the invention to obtain finished granulesfor bottles, so that a further processing of the slightly modified PETchips into bottles to be filled with soft drinks, water or other fillingmaterials was easily possible. The results are shown in Tables 2.1 and2.2.

Material used in Example 3, Table 2.1

Catalyzer content antimony (Sb): 250 ppm, phosphor content: 50 ppm,cobalt: 25 ppm, blue dye: 1.0 ppm, IPA: 2.0% by wt. DEG: 13.% by wt.TABLE 2.1 Example 3 2. 1. Crystallization Crystallization (zones 3 to 5)(zones 1 und blade type Material used: 2) crystallizer spherical chipfluidized bed VWZ: 180 min shape crystallizer T: 215° C. catalyzer: 250ppm VWZ: 60 min. Delta I.V. = 0.017 Analyses Sb T: 200° C. [dl/g] I.V.[dl/g] 0.804 0.799 0.812 COOH 22 20 18 [mmol/kg] DSC 248/152/79 Tm/Tk/Tg[° C.] Color 76 85 86.5 Color a −2 −1.7 −1.5 Color b −5.5 −3.3 −2 AA[ppm] 80 15 3.2 KTG [° C.] — 47.1 52.6 AA- 9.5 reformation [ppm] Dust<10 <10 <10 [ppm]

Material used in Example 4, Table 2.2

Catalyst content ECOCAT B®: metal 5 ppm, phosphor content:10 ppm,blue/red dye: 1.5/1.25 ppm, IPA :2.0% by wt., DEG:1.3% by wt. TABLE 2.2Example 4 2. 1. Crystallization Crystallization (zones 3 to 5) Materialused (zones 1 and shaft type spherical chip 2) crystallizer formfluidized bed VWZ: 180 min/ catalyzer: crystallizer T: 215° C. ECOCATB ® VWZ: 60 min./T: delta I.V. = 0.032 Analyses 5 ppm metal 200° C.[dl/g] I.V. [dl/g] 0.795 0.797 0.827 COOH 15 14 13 [mmol/kg] DSC248/152/79.5 Tm/Tk/Tg [° C.] Color L 72 81 84 Color a −3.5 −2.2 −2 Colorb 1.4 1.7 1.9 AA [ppm] 40 7.9 0.8 KTG [° C.] — 47.8 52.7 AA- 8.9reformation [ppm] Dust <10 <10 <10 [ppm]

1. A method for producing polyesters, comprising crystallization of apolyester material, the crystallization being carried out in two stages,wherein in the first stage partly crystalline polyester material isprovided, and in the second stage the partly crystalline polyestermaterial flows at temperatures suited for crystallization (i) undermechanical disturbance and gas in countercurrent flow, (ii) undermechanical disturbance and gas in concurrent flow, and (iii) withoutmechanical disturbance and gas in concurrent flow.
 2. The methodaccording to claim 1, wherein the partly crystalline polyester materialprovided in the first stage has a degree of crystallization of about 40to 48%.
 3. The method according to claim 1, wherein the partlycrystalline polyester material is provided in the first stage bytreating the polyester material by vortexing in a gas flow and at risingtemperatures of about 170 to about 210° C. at a residence time of up toabout 30 min.
 4. The method according to claim 3, wherein the vortexingof the polyester material is carried out in a fluidized bedcrystallizer.
 5. The method according to claim 4, wherein in the firststage vortexing is carried out in a first zone in a fluidized bed withmixing properties and in a second zone in a fluidized bed withcontrolled granulate flow.
 6. The method according to claim 5, whereinvortexing with gas is carried out at a gas rate of about 3.2 to 4 m/s inthe first zone and at a gas rate of about 2.1 to 2.7 m/s in the secondzone.
 7. The method according to claim 1, wherein the temperature usedin the second stage is about 190 to about 220° C.
 8. The methodaccording to claim 1, wherein the residence time in the second stage (i)is about 30 to about 60 min, in the second stage (ii) about 30 to about60 min, and in the second stage (iii) about 60 to about 180 min.
 9. Themethod according to claim 1, wherein the second stage is carried out ina shaft type crystallizer.
 10. The method according to claim 1, whereinthe polyester material used is granulate.
 11. The method according toclaim 2, wherein the total residence time of the polyester material inthe first and second stage is about 100 to 350 min.
 12. The methodaccording to claim 2, wherein the residence time ratio of the polyestermaterial in the first stage to the second stage is about 1:4 to 1:32.13. The method according to claim 1, wherein the polyester material usedduring crystallization has an I.V. of at least 0.3 dI/g.
 14. A methodfor producing polyester molded articles comprising using a polyestermaterial that is obtainable according to claim 1 without a solid-statepolycondensation to form a polyester molded article.
 15. The methodaccording to claim 14, wherein the polyester molded articles areselected from the group consisting of bottles, sheets, films, and hightenacity technical filaments.
 16. Apparatus for crystallizing polyestermaterial in granulate form, comprising three successive sections atleast one inlet opening provided in the first section, at least oneoutlet opening provided in the third section, a means for effectingmechanical disturbance of the polyester material provided in the firstand second sections, at least one gas inlet opening arranged in thetransitional area between first and second section, and at least one gasoutlet opening provided in both the first and third section.
 17. Theapparatus according to claim 16 in which the means comprises a shaft onwhich at least one arm is provided.
 18. The apparatus according to claim16, in which the means for effecting mechanical disturbance of thepolyester material comprises a first shaft and a second shaft, at leastone arm being provided on each shaft.
 19. The method according to claim10, wherein the polyester material is spherical granulate.